Off-the-road pneumatic tire with specified bead area design

ABSTRACT

An improved off-the-road pneumatic tire designed to be mounted on an associated design rim having a flange portion is described. The rim flange has an axially inward surface contacting the axially outward portion of the bead area of the tire. Each bead portion has a surface contacting a radially inner portion of the rim flange. The surface and the flange initially cease contact and diverge from one another at a location in the cross-section of the tire and rim and in a region of the flange in which a line L1 tangent to the flange surface and passing through the axis forms an angle greater than 0° and less than or equal to 15° with a radial line L2 passing through the point of divergence and perpendicular to the axis. The tire has a steel reinforced radial ply which extends between and wraps about each bead. The ply has an inflection point located radially between a radially outward surface of the bead and a radially outward surface of the rim flange portion.

This is a division of application Ser. No. 08/153,726 now U.S. Pat. No.5,429,168, filed Nov. 16, 1993.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to off-the-road large pneumatic tires, such asare commonly used on earthmoving equipment, and more particularly tolarge pneumatic tires having a specified clearance relationship betweenthe lower bead area of the tire and a flange portion of an associatedrim upon which the tire is designed to be mounted.

2. Description of the Related Art

Large pneumatic tires to be used on earthmoving equipment, commonlyknown as earthmover tires, are well-known. Earthmover tires are requiredto perform in difficult environments. When used "off-the-road", they arerequired to provide excellent traction for extremely heavy vehiclespushing, pulling and lifting extremely heavy loads. The environment isalso fraught with rocks and other sharp instruments which can damage thetires. Due to the relatively high cost of these large tires, durabilityand long life is a primary design parameter.

A second environment in which the tires might be expected to form isthat of public highways. Sometimes the earthmoving equipment must travelon public highways as the vehicles travel from construction site toconstruction site.

Previously, the required strength was built into such tires through theincorporation of certain curves into the molded shape of the exterior ofthe tire. These extra curves or bulges were believed to give extrasupport to those areas of the tire where durability was especiallyimportant, such as the lower sidewall, mid sidewall and tread center. Inthe bead flange area, the prior art off-the-road tires employed aninterference fit whereby the tire was in contact along the radiallyouter surface of the rim flange. Off-the-road tire engineersconventionally add mass to structurally improve the durability of thetire.

In the aircraft tire art, tire engineers must always look to reducedmass, due to the unique weight limitations of that art's area, yet thetires must still be durable.

In U.S. Pat. Nos. 4,790,364 and 4,813,467, an aircraft tire and rimcombination is disclosed which shows a clearance between a rim flangeand the surface of the bead portion of the tire. However, theseinventions concern aircraft tires which are much different inconstruction and application than earthmover tires. They are alsodesigned to be used on aircraft rims, such as H-type rims, which aredifferent in design than earthmover or off-the-road rims. In addition,the tires shown in U.S. Pat. Nos. 4,790,364 and 4,813,467 do not haveinflection points in the ply, as does the present invention.

The present invention also has as one of its objects improved durabilityin the earthmover tire, but does so by providing a bead area designwhich has demonstrated a marked improvement over the prior art.

It is therefore an object of the invention to provide an earthmover tirehaving improved durability.

It is another object of the invention to provide an earthmover tirehaving a bead portion which cooperates with a flange portion of anassociated rim to improve the durability of the tire.

It is a further object of the invention to provide an earthmover tirehaving a certain relationship between the bead flange area of the tireand the rim flange, such relationship creating a clearance therebetween.The nature of the clearance is discussed herein and meets certainrequirements in order to provide the durability sought.

SUMMARY OF THE INVENTION

An improved off-the-road pneumatic tire is disclosed. The improvedpneumatic tire has a nominal rim diameter of at least 50 centimeters (20inches), an axis of rotation, and a carcass having a pair of beadportions. Each bead portion has an annular inextensible bead and a beadportion. The carcass further includes a steel-reinforced radial plyextending between and wrapped around each bead. The ply has turn-up endsextending axially and radially outwardly from each bead and a pluralityof reinforcing belts disposed radially outwardly of the ply. A tread isdisposed radially outwardly of the carcass. Each bead portion has aradially inner first surface and a radially outwardly extending secondsurface. The first and second surfaces of the bead portion beingdesigned to engage a design rim as specified by the applicable standardsorganization. The rim having a pair of bead seat portions and a pair offlange portions respectively. Each bead portion has the first surfacecontacting the bead seat portion of the rim and the radially outwardlyextending second surface contacting a radially inner portion of the rimflange portion. When the tire is mounted onto the rim, uninflated andunloaded, the second surface and the flange initially cease contact anddiverge from one another at a location in the cross-section of the tireand rim and in a region of the flange in which a line L1 tangent to theflange surface and passing through the axis forms an angle in the rangeof greater than 0° to 15° with a radial line L2 passing through thepoint of divergence and perpendicular to the axis.

In a preferred embodiment, the line L1 forms an angle in the range ofgreater than 2° and equal to or less than 15° with the radial line L2.

According to another aspect of the invention, the tire is furthercharacterized by the ply having an inflection point, the inflectionpoint radially being between a radially outer surface of the bead and aradially outer surface of the flange portion of the rim.

According to another aspect of the invention, the second surface of thebead flange is defined by a radius R1 and the radially inner portion ofthe rim flange portion is defined by a radius R2, R1 and R2 halvingcenters along a line parallel to the axial centerline of the tire, R1being greater than R2 and being equal to or less than 1.3 R2.

According to another embodiment of the invention, the tire has athickness T1 of rubber axially and radially inwardly of the ply. Thethickness T1 is 1.5% and 3.5% of the tire's section width. The inserthas a thickness which is between 50% and 75% of T1 inwardly of the ply.

Still other benefits of the invention will become apparent to thoseskilled in the art upon a reading and understanding of the followingdetailed description of the invention.

DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangementsof parts, a preferred embodiment of which will be described in detail inthis specification and illustrated in the accompanying drawings whichform a part hereof and wherein:

FIG. 1 is a cross-sectional view illustrating one side or one half ofsymmetrical earthmover tire according to the invention;

FIG. 2 is an enlarged cross-sectional view illustrating the bead portionof the tire of FIG. 1;

FIG. 3 is a cross-sectional view of the bead portion of a tire accordingto a second embodiment of the invention;

FIG. 4 is an enlarged cross-sectional view of the tire shown in FIG. 3;

FIG. 5 is a schematic view of the geometric relationship between anaxially outward portion of the bead portion of the tire and the flangeportion of the rim;

FIG. 6 is a schematic view of an inflection point in the ply line of anearthmover tire according to the invention;

FIG. 7 is a schematic view of a tire sidewall according to theinvention;

FIG. 8 is a schematic view of a further geometric relationship betweenthe bead portion of the tire and the flange portion of the rim;

FIG. 9 is a cross-sectional view of a typical bead as used in earthmovertires;

FIG. 10 is a cross-sectional view of a bead as used in a secondembodiment of earthmover tires according to the invention; and,

FIG. 11 is a cross-sectional view of one-half of a symmetricalearthmover tire according to the invention, shown to illustrate varioustire parameters.

DEFINITIONS

"Aspect ratio" of the tire means the ratio of its section height (SH) toits section width (SW);

"Axial" and "axially" means lines or directions that are parallel to theaxis of rotation of the tire;

"Bead" means that part of the tire comprising an annular tensile memberwrapped by ply cords and shaped, with or without other reinforcementelements such as flippers, chippers, apexes, toe guards and chafers, tofit the design rim;

"Belt reinforcing structure" means at least two layers of plies ofparallel cords, woven or unwoven, underlying the tread, unanchored tothe bead, and having both left and right cord angles in the range from17 degrees to 27 degrees with respect to the equatorial plane of thetire;

"Carcass" means the tire structure apart from the belt structure, tread,under tread, and sidewall rubber over the plies, but including thebeads;

"Circumferential" means lines or directions extending along theperimeter of the surface of the annular tread perpendicular to the axialdirection;

"Chafers" refers to narrow strips of material placed around the outsideof the bead to protect cord plies from the rim, distribute flexing abovethe rim, and to seal the tire;

"Chippers" means a reinforcement structure located in the bead portionof the tire;

"Cord" means one of the reinforcement strands of which the plies in thetire are comprised;

"Design rim" means a rim having a specified configuration and width. Forthe purposes of this specification, the design rim and design rim widthare as specified by the industry standards in effect in the location inwhich the tire is made. For example, in the United States, the designrims are as specified by the Tire and Rim Association. In Europe, therims are as specified in the European Tyre and Rim TechnicalOrganisation--Standards Manual and the term design rim means the same asthe standard measurement rims. In Japan, the standard organization isThe Japan Automobile Tire Manufacturer's Association.

"Equatorial plane (EP)" means the plane perpendicular to the tire's axisof rotation and passing through the center of its tread;

"Footprint" means the contact patch or area of contact of the tire treadwith a flat surface at zero speed and under normal load and pressure;

"Innerliner" means the layer or layers of elastomer or other materialthat form the inside surface of a tubeless tire and that contain theinflating fluid within the tire;

"Net-to-gross ratio" means the ratio of the tire tread rubber that makescontact with the road surface while in the footprint, divided by thearea of the tread in the footprint, including non-contacting portionssuch as grooves;

"Normal rim diameter" means the average diameter of the rim flange atthe location where the bead portion of the tire seats;

"Normal inflation pressure" refers to the specific design inflationpressure and load assigned by the appropriate standards organization forthe service condition for the tire;

"Normal load" refers to the specific design inflation pressure and loadassigned by the appropriate standards organization for the servicecondition for the tire;

"Ply" means a continuous layer of rubber-coated parallel cords;

"Radial" and "radially" means directions radially toward or away fromthe axis of rotation of the tire;

"Radial-ply tire" means belted or circumferentially-restricted pneumatictire in which the ply cords which extend from the bead to bead are laidat cord angles between 65 degrees and 90 degrees with respect to theequatorial plane of the tire;

"Section height" (SH) means the radial distance from the nominal rimdiameter to the outer diameter of the tire at its equatorial plane; and,

"Section width" (SW) means the maximum linear distance parallel to theaxis of the tire and between the exterior of its sidewalls when andafter it has been inflated at normal pressure for 24 hours, butunloaded, excluding elevations of the sidewalls due to labeling,decoration or protective bands.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 1 and 2, a cross-sectional view of one half ofearthmover tire 10 according to the invention is illustrated.

The tire 10 has a tread 12 disposed over the crown region of the tirecarcass 14. The carcass 14 has a pair of inextensible annular beads 16.The illustrated beads 16 are of hexagonal cross-sectional shape,although alternate bead designs will also be disclosed herein. Wrappedabout the beads 16 is a steel cord reinforced ply 18. Disposed radiallyoutwardly of the ply 18 is a steel reinforced belt package 20 consistingof at least four belts. A pair of sidewalls 22 extend between the tread12 and the bead area. Above the bead 16 is an elastomeric apex 24.Wrapped around the bead is a flipper 26. The flipper 26 is adjacent thebead 16 and the carcass ply 18. Outward of the ply turn-up 28 are cordreinforced chippers 30. The radially inner portion of the carcass 14includes an air impermeable inner liner 36. Adjacent the inner liner 36is an elastomeric ply line insert 50.

The tire 10 has a flat tread arc at the centerline (CL) of the tread 12in the area marked TC. The tread 12 includes a plurality of radiallyouter ground-contacting lugs 44 and an inner tread 46.

In the preferred embodiment, the ground-contacting lugs 44 have aradially outer ground contacting surface 48 having an area in the rangeof 40% to 60% of the overall tread area. This relationship of theground-contacting area of the tread to the other portions of the treadis commonly referred to as the "net-to-gross ratio."

With reference to FIG. 11, certain standard tire parameters will bedefined with reference to an off-the-road tire 10. The carcass 14 hasthe steel cord reinforced ply oriented along a path commonly known asthe "ply line." As illustrated in FIG. 11, the ply line is located atthe minimum centerline gauge at the tire centerline. From this data, theRhoM line can be determined. The actual radii and tangency points aredefined geometrically from specific tire envelope and constructionperimeters. The design requires the following data prior to defining thegeometry: Bead size, tread line centerline depth required engages of allcomponents at the tread centerline. The maximum section width (SW) andoutside diameter (OD) are determined, as is the tire bead size anddimensions, according to conventional methods. Then RhoM is defined byfinding the center point between the ply line bead pivot point (4:5degrees) from the bead center at the ply line centerline and the plyline centerline at the tire radial centerline. To calculate RhoM, onemust first locate two points on the tire: the ply line pivot point (P)and ply line centerpoint (C). The ply line pivot point is located at theintersection of the ply line centerline and a line (Lp) drawn at anangle A of 45 degrees relative to the axis of rotation and extendingfrom the bead center.

The ply line centerpoint (C) is located at the ply line centerline atcross-sectional centerline (CL). In the preferred embodiment, this pointis located at the cross-sectional centerline (CL) at the minimum gauge(MG) to the top of the reinforcing ply plus one half of the ply gauge.The minimum gauge (MG) is determined for a given tire by summing thefollowing: 1) desired tread depths; 2) required under tread gauge; 3)reinforcing belt gauges; 4) any insulating gum layers between the abovecomponents; and 5) one half of the thickness of the ply 18.

A line extending between these points defines the line (PC). At themidpoint of the PC line, parallel to the axis of rotation of the tire isthe RhoM line. The distance from the tire's axis of rotation (AR) andthe RhoM line is RhoM (or the midline radius). The description of theply line and other tire geometry parameters are discussed in more detailin copending U.S. patent application Ser. No. 07/999,255, now U.S. Pat.No. 5,261,474, which is incorporated herein by reference.

With reference to FIGS. 3 and 4, an alternate embodiment of theinvention is disclosed. All components of the invention are the same asthat disclosed in FIGS. 1 and 2 with the exception of the bead 16. Inthe embodiment shown in FIGS. 3 and 4, the radially outer half of thebead 54 has a hexagonal configuration while the radially inner half ofthe bead 54 is approximately semicircular.

With reference to FIGS. 9 and 10, a third embodiment of a bead isillustrated. In FIG. 9, a bead 86 as is used in the improved tire iscompared to a bead 88 which is used in some embodiment of the improvedtire. Bead 86 has a height of 2.52 inches while bead 88 is a truncatedhexagon in cross-section with a radially outer section of the bead beingtruncated and has a height of only 1.77 inches, approximately 70% theheight of bead 86.

With reference to FIG. 5, another important aspect of the invention willbe explained. In FIG. 5, the radially and axially outer surface 58 of abead portion 90 of a tire 10 near its interface with a flange portion 60of a rim 92 is schematically shown. The flange portion 60 has a radiallyand axially inner portion 62 which contacts the outer surface 58 of thebead portion 90 of the tire 10. In the improved tire 10, a clearance 66is created by a relationship between R1, which is the radius of theouter surface 58 of the bead portion 90, and R2, which is the radius ofthe flange portion 60 of the rim 92. According to the invention, R1 isequal to or greater than 1.3 R2. The center 68 of R2 and the center 70of R1 are located along a line 74 which is parallel to the tire's axisof rotation. The line 74 is equal to G minus R2, and is a standard inthe industry as defined by the 1993 Tire and Rim Association handbook.In the preferred tire 10, a 36.00R51 earthmover tire, the clearance 66so created is between 0.08 inches and 0.12 inches, with the preferredclearance 66 being 0.10 inches.

With reference to FIG. 6, a further aspect of the invention will beillustrated. In FIG. 6, the bead 16, flange portion 60 of the rim 92 andply 18 are schematically illustrated. The radially outermost surface offlange portion 60 is indicated by line 76. Line 78 represents theradially outermost surface of the bead 16. An inflection point 80 in theline of the ply 18 indicates the point where the inflection of thecurved ply 18 changes. The portions of the ply 18 radially outwardly ofthe inflection point 80 are described by a radius R+ having its centeraxially and radially within the tire 10. Points on the ply 18 radiallyinwardly of inflection point 80 are described by radius R- which has itscenter axially and radially outwardly of the ply 18. In the improvedtire 10, the inflection point 80 is located along the ply 18 radiallyoutwardly of the radially outermost portion of the bead 16, i.e. line 78and radially inwardly of the radially outermost portion of the flangeportion 60, i.e. line 76.

With reference to FIG. 7, a still further aspect of the invention willbe illustrated. FIG. 7 is a schematic illustration of an enlargedportion of a tire near its RhoM. The portion of the tire 10 shown inFIG. 7 is essentially the area shown on FIG. 1 between lines 7--7. Theinsert 50 has a thickness T1 of material axially and radially inwardlyof the ply 18. The thickness T1 is between 1.5% and 3.5% of the tire'ssection width (SW). The insert 50 has a thickness T2 which is between50% and 75% of T1.

With reference to FIGS. 2 and 8, a still further aspect of the inventionwill be illustrated. The bead portion 90 of the tire 10 has a radiallyinner first surface 96 and a radially outwardly extending second surface98. The first and second surfaces 96, 98 of the bead portion 90 aredesigned to engage a design rim 92 as specified by the applicablestandards organization. Currently, such a standards organization is theTire & Rim Association Handbook. The rim 92 includes a pair of bead seatportions 102 and a pair of flange portions 60 respectively. The improvedtire 10, when normally mounted uninflated and unloaded, is characterizedby each bead portion 90 having the first surface 96 contacting the beadseat portion 102 of the rim and the radially outwardly extending secondsurface 98 contacting a radially inner portion 106 of the rim flangeportion 60. The second surface 98 of the bead portion 90 and the flange60 initially ceasing contact and diverging from one another at alocation in the cross-section of the tire 10 and rim 92 and in a regionof the flange 60 in which a line L1 tangent to the flange surface 106and passing through the axis of the tire 10 forms an angle greater than0° and less than or equal to 15° with a radial line L2 passing throughthe point of divergence 110 and perpendicular to the axis of the tire10. The line L1 forms an angle α in the range of greater than 0° andequal to or less than 15° with the radial line L2. In a preferredembodiment, the line L1 forms an angle in the range of greater than 2°and equal to or less than 15° with the radial line L2.

Tires incorporating the above-described features have proven to be moredurable than prior art designs. For example, tires incorporating theinventive features described herein demonstrated a 51.3% improvement inlower sidewall cyclic distortion energy density measurements (DEDs).These energy measurements are a accurate indicator of strain energydensity in tire designs. It was found that the reduced interference withthe rim flange was the largest contributor to this improvement.

Sidewall surface strains were reduced from 13.2% in the controlconstruction tire to 11.8% in the tire incorporating the inventivefeatures. The reduction in sidewall strains was directly attributable tothe presence of the inserts 50. When the inserts were removed from theexperimental tires, the sidewall surface strains increased up to 13.1%,essentially identical to the 13.2% sidewall surface strains found in thecontrol tire construction.

The invention has been described with reference to a preferredembodiment. Obviously, modifications and alterations will occur toothers upon a reading and understanding of this specification. It isintended to include all such modifications and alterations insofar asthey come within the scope of the appended claims or the equivalentsthereof.

Having thus described the invention, it is now claimed:
 1. An improvedoff-the-road pneumatic tire, the tire having a nominal rim diameter ofat least 50 cm (20 inches), an axis of rotation, a carcass having a pairof bead portions, each bead portion having one annular inextensiblebead, the carcass further including a steel-reinforced radial plyextending between and wrapped about each bead, the ply having turn-upends extending axially and radially outwardly from each bead; aplurality of reinforcing belts disposed radially outwardly of the ply; atread disposed radially outwardly of the carcass; the bead portionhaving a radially inner first surface and a radially outwardly extendingsecond surface, the first and second surfaces of the bead portion beingdesigned to engage a design rim as specified by the applicable standardsorganization, the rim having a pair of bead seat portions and a pair offlange portions respectively; the improved tire when normally mounted onthe rim, uninflated and unloaded, being characterized by:the ply havingan inflection point, the inflection point in each bead portion beingradially between a radially outer surface of the bead and a radiallyouter surface of the rim flange portion.
 2. The pneumatic tire of claim1 wherein the second surface of the bead portion is defined by a radiusR1 and the radially inner portion of the rim flange portion is definedby a radius R2, R1 and R2 having centers along a line parallel to theaxial centerline of the tire, R1 being greater than R2 and being equalto or less than 1.3 R2.
 3. The pneumatic tire of claim 1 wherein thebead is a truncated hexagon in cross-section with a radially outersection of the bead being truncated, the bead having a height ofapproximately 70% of that of the corresponding hexagonal bead.
 4. Thepneumatic tire of claim 1 wherein the tire has a thickness T1 of rubberaxially and radially inwardly of the ply, the thickness T1 being between1.5% and 3.5% of the tire's section width, the tire further comprisingan insert axially and radially inwardly of the ply, the insertcomprising portion of the rubber having a thickness T1, the inserthaving a thickness T2 wherein T2 is between 50% and 75% of T1.
 5. Thepneumatic tire of claim 4 wherein the second surface of the bead portionis defined by a radius R1 and the radially inner portion of the rimflange portion is defined by a radius R2, R1 and R2 having centers alonga line parallel to the axial centerline of the rim, R1 being greaterthan R2 and being equal to or less than 1.3 R2.